b'depletion; 3) and the outmost regionPu migration extend approximatelyFigure 4. Elemental WDX with a U-Pu-Zr composition similar to50 m into the cladding and Fe andmaps obtained by EPMA on the as fabricated alloy. The redistribu- Ni was found up to approximatelythe cladding-fuel interface, tion of these main elements is strongly100 m into the fuel. Finally, onlyshowing FCCI.influenced by the temperaturea minor presence of volatile fission gradient. Thus, the spatial compositionproducts (e.g., Cs and Xe) was found data coupled to known phase diagramin the foam region, inconsistent and modeling, will provide insightwith previous indications from into possible phases formed and thegamma spectroscopy on the pin. temperature reached in the variousThe nonaqueous sample preparation regions. Moreover, the region withmethod is believed to not be low Zr concentration is of particularsuccessful in retaining the formed interest for fuel performance due tochemical compound, as Na was the presence of phases with lowerconcomitantly wash out during solidus temperature. sample preparation.Fuel Cladding Chemical InteractionBy these analyses we can conclude (FCCI, Figure 4) was also investigatedthat the samples behaved in line with in this specimen, as this phenomenonsteady state irradiation of metallic is considered a limiting factor tofuel, preliminary indicating that the fuel performance and influencesmoderate transient ramps did not the performance limits of the fuelinfluence the fuel performance. These during transient conditions. FCCI wasanalyses confirmed safety of this fuel observed in a limited area at the topform even under unplanned events.of the fuel, where lanthanides and 2019|AFC ACCOMPLISHMENTS 223'